As pressure sensors are elements for measuring pressure in a certain system, the pressure sensors are widely used in various applications including an industrial instrumentation, an automatic control, a medical device, motor engineering apparatuses, an environment control, and an electrical apparatus applications, etc. The measurement principle of the pressure sensors is based on measuring electrical variations due to displacement or deformation, etc, and various types of the sensors are implemented.
Types of the pressure sensors include a mechanical pressure sensor using the Bourdon tube or bellows, a pressure-resistive electronic pressure sensor using a strain gauge, and a capacitive electronic pressure sensor for measuring variations of electrostatic capacitance between two objects, etc. In particular, since the pressure-resistive electronic pressure sensor using strain gauge has superiority in view of performance or price, it has become the most frequently used sensor.
The term “strain” is used to indicate deformity or a deformation rate, represents a proportion of the stretched or shortened length to the original length of the object when the object is elongated or compressed, and is used in applications including civil engineering, aeronautical engineering, and electronics, etc, which deal with an analysis of a structure or a mechanical component when the structure or the component is deformed by an external force. The strain gauge is a gauge which is attached to a surface of the structure to measure the state and the amount of deformation of the structure, and includes an electric strain gauge which measures the amount of deformation of the structure as resistance and a mechanical strain gauge which measures the variation of the length of the structure being deformed.
An element of the electric stain gauge uses metals having large resistance variation, and in this case, a resistance line made in the form of wire or foil on an insulator is used to measure resistance.
The sensor with the strain gauge prevents failures in machinery or safety accidents, and enables the user to be informed of an accident and to respond accordingly. The smaller the sensor becomes, the more efficiently the space can be used without affecting other driving parts.
However, the pressure sensor can only measure the deformation rate caused by pressure applied in a perpendicular direction on the structure, and thus it is difficult to measure a deformation rate caused by pressure applied in a parallel direction on the structure.
Further, since it is required to have a separate deforming structure to measure the deformation rate caused by a shearing force, there is a problem in that overall size of the sensor increases. Thus, there is a need to provide a sensor that is small in size and can measure both of the deformation rates caused by pressure or shear force.